Electro-optic displays, and components for use therein

ABSTRACT

A method and system for forming filter elements on a plurality of display substrates using a digital imaging system operable to selectively deposit filter material at a plurality of deposition locations is disclosed. The method involves receiving orientation information defining a disposition of a plurality of pixels associated with the at least one display substrate, identifying pixels in the plurality of pixels that are to receive filter material for forming a filter element on the pixel, selecting deposition locations within each of the identified pixels in accordance with the orientation information to meet an alignment criterion associated with placement of the filter element within the pixel, and controlling the digital imaging system to cause deposition of the filter material at the selected deposition locations. A method and system for forming filter elements on a substrate is also disclosed, which involves selecting locations to receive filter material for forming filter elements on the substrate, introducing a random variation in placement of the filter elements, and forming filter elements at the selected locations, the substrate being subsequently aligned to a display substrate for forming a display. A method and system for forming filter elements on a display substrate is also disclosed, which involves selectively depositing filter material to form the filter elements on a plurality of pixels associated with the display substrate, and selectively exposing the deposited filter material to thermal laser radiation to condition the deposited filter material.

RELATED APPLICATIONS

This application claims the benefit of provisional patent application61/400,291 entitled “METHOD FOR PRODUCING COLOR FILTERS ON MULTIPLEREFLECTIVE DISPLAYS WITH HIGH ACCURACY AND THROUGHPUT”, filed on Jul.26, 2010 and incorporated herein by reference in its entirety. Thisapplication also claims the benefit of provisional patent application61/402,234 entitled “METHOD FOR ENHANCING SURFACE PROPERTIES OFMATERIALS THERMALLY TRANSFERRED USING LASER IMAGING”, filed on Aug. 26,2010 and incorporated herein by reference in its entirety. Thisapplication also claims the benefit of provisional patent application61/520,138 entitled “METHOD FOR USING THE BIDIRECTIONAL NATURE OF A FLATBED IMAGER TO INCREASE THROUGHPUT OF TILED IMAGING OF REFLECTIVEDISPLAYS”, filed on Jun. 6, 2011 and incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to electronic displays and moreparticularly to forming filter elements on display substrates.

2. Description of Related Art

Electronic displays are used to produce visual output for a number ofelectronic devices such as television and computer monitors, mobilecommunication devices, and electronic book devices (e-Readers), forexample. Various types of electronic displays are commonly used,including liquid crystal displays (LCD), Organic Light Emitting Diodedisplays, Electro-wetting displays, and Electrophoretic displays, forexample.

LCD displays are an example of a transmissive display that utilizes acolor filter to turn what is effectively a monochromatic display into acolor display. A thin film transistor (TFT) layer and a color filterlayer are generally separately manufactured on glass substrates, whichare subsequently aligned and assembled into a display unit. The TFTlayer includes a plurality of drivers, each driver being operable tocontrol a small area of the display or picture element (pixel). Thecolor filter layer generally includes red, green, and blue color filterelements that overlay the display pixels and filter the white light todisplay a color image.

Color filters for LCD displays have been predominantly produced usingphotolithographic techniques, but thermal laser transfer of colorants orinkjet transfer of colorants onto a color filter glass substrate or evendirectly onto the TFT layer have also been attempted. By transferringcolorants directly onto the TFT layer, the need for subsequent precisionalignment of the color filter to the TFT layer is avoided.

Electrophoretic displays are an example of a reflective displays, inwhich ambient light provides illumination and display pixels areelectronically controlled by an underlying TFT to selectively reflectthe ambient light to form a display image. Like LCD displays,electrophoretic displays are also essentially monochrome displays. Inorder to provide a color display, color filter elements may be formedover the reflective display pixels. The color filter elements may coversubstantially the entire area of the associated reflective displaypixel, or may only cover a portion of the area.

There remains a need for improved methods and apparatus for formingcolor filters.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided amethod for forming filter elements on at least one display substrateusing a digital imaging system operable to selectively deposit filtermaterial at a plurality of deposition locations. The method involvesreceiving orientation information defining a disposition of a pluralityof pixels associated with the at least one display substrate,identifying pixels in the plurality of pixels that are to receive filtermaterial for forming a filter element on the pixel, selecting depositionlocations within each of the identified pixels in accordance with theorientation information to meet an alignment criterion associated withplacement of the filter element within the pixel, and controlling thedigital imaging system to cause deposition of the filter material at theselected deposition locations.

Each identified pixel may have associated extents within which thefilter element is to be to be placed and the alignment criterion mayinvolve a threshold value representing a permitted deviation inplacement of the filter element with respect to the extents andselecting may involve selecting deposition locations to causesequentially shifted placement of the filter element with respect to theextents in subsequent identified pixels while the sequentially shiftedplacement remains within the threshold value. Selecting may furtherinvolve selecting deposition locations to cause placement of the filterelement to be shifted within the threshold value when the sequentiallyshifted placement exceeds the threshold value.

Selecting deposition locations to cause placement of the filter elementto be shifted back within the threshold value may involve selectingdeposition locations that are shifted with respect to the extents by atleast a spacing between adjacent deposition locations.

The method may involve introducing a random variation in the thresholdvalue, the random variation being operable to disrupt regular patternsthat occur in filter element placement due to the sequentially shiftedplacement of the filter elements in the subsequent pixels.

Identifying the pixels may involve identifying pixels in the pluralityof pixels to receive one of a plurality of colored filter materials, andselecting the deposition locations may involve selecting depositionlocations to cause placement of the filter element to be varied betweeneach of the plurality of colored filter materials to disrupt regularpatterns that occur in filter element placement due to the sequentiallyshifted placement of the filter elements in the subsequent pixels.

The deposition locations may include first deposition locationsgenerally aligned along a first axis of the display substrates, andsecond deposition locations generally aligned along a second axis of thedisplay substrates, the second deposition locations being more closelyspaced than the first deposition locations, and each identified pixelmay have associated first axis extents in a direction of the first axisand associated second axis extents in a direction of the second axis,the first and second axis extents defining an area within which thefilter element is to be placed, and selecting may involve selecting thefirst deposition locations to provide increased spacing between thefilter element and the first axis extents, and selecting the seconddeposition locations to provide reduced spacing between the filterelement and the second axis extents, such that the selection of firstand second deposition locations together meets a coverage criterionassociated with the filter element.

The selecting may further involve introducing a random variation inplacement of the filter element, the random variation being operable todisrupt regular patterns that occur in filter element placement due tothe selecting.

Introducing the random variation in placement of the filter element mayinvolve introducing a random variation in the selecting of the firstdeposition locations such that the increased spacing in the first axisdirection varies randomly between subsequent identified pixels, and theselecting of the second deposition locations may involve selectingsecond deposition locations to meet the coverage criterion associatedwith the filter element.

The first deposition locations may be associated with actuating ones ofa plurality of individually actuable channels, the individually actuablechannels being generally aligned along a first axis and operablyconfigured to cause deposition of the filter material at selecteddiscrete deposition locations associated with the channels.

The individually actuable channels may be provided by one of a laserradiation source operably configured to generate a plurality ofindividually actuable laser beams, the laser beams being selectivelyoperable to cause deposition of filter element material from a filtermaterial donor sheet onto the at least one display substrate, and aplurality of ink jet nozzles for depositing filter element material ontothe at least one display substrate.

The second deposition locations may be associated with causing relativedisplacement between the display substrates and the digital imagingsystem in a direction generally aligned with the second axis therebyfacilitating deposition of the filter material at selected depositionlocations disposed in a swath extending along the second axis.

The selecting may further involve introducing a random variation inplacement of the filter element, the random variation being operable todisrupt regular patterns that occur in filter element placement in theidentified pixels on each display substrate due to a spacing betweenadjacent deposition locations.

Identifying the pixels may involve randomly identifying pixels in theplurality of pixels to receive one of a plurality of colored filtermaterials to cause resulting filter elements of each color to berandomly dispersed across each display substrate.

The at least one display substrate may include at least two displaysubstrates and the deposition locations may include first depositionlocations generally aligned along a first axis of the at least twodisplay substrates and second deposition locations generally alignedalong a second axis of the at least two display substrates, and the atleast two display substrates may be disposed in succession along thesecond axis, and receiving the orientation information may involvereceiving information defining the disposition of the plurality ofpixels associated with each of the at least two display substrates withrespect to the first and second axes, and the method may further involvecomputing an offset associated with the plurality of pixels in adirection of the first axis for at least one of the at least two displaysubstrates, determining a residual portion of the offset that cannot becompensated by the selection of the deposition locations, andcontrolling the digital imaging system may involve causing relativedisplacement between the at least two display substrates and the digitalimaging system in a direction of the second axis, and causing thedigital imaging system to be repositioned in a direction of the firstaxis relative to the at least two display substrates by the residualportion of the offset associated with the at least one display substrateto position the digital imaging system for deposition of the filtermaterial on the at least one of the at least two display substrates.

Causing the digital imaging system to be repositioned may involvecausing the digital imaging system to be repositioned while movingbetween the at least two display substrates.

Causing relative displacement between the at least two displaysubstrates and the digital imaging system in the direction of the secondaxis may involve alternating between causing relative displacements in afirst pass in a first direction aligned with the second axis and asecond pass in a second direction opposite to the first direction, andcontrolling the digital imaging system may involve controlling thedigital imaging system to cause deposition of the filter material on afirst of the at least two display substrates on the first pass and asecond of the at least two display substrates on the second pass andcausing the digital imaging system to be repositioned may involvecausing the digital imaging system to be repositioned while changingdirection between the first pass and the second pass.

The at least two display substrates may include more than two displaysubstrates disposed in succession along the second axis and controllingthe digital imaging system may involve controlling the digital imagingsystem to cause deposition of filter material on alternate ones of themore then two display substrates on the first pass and remaining ones ofthe more than two display substrates on the second pass and causing thedigital imaging system to be repositioned may involve further causingthe digital imaging system to be repositioned while disposed between atleast one of the alternate ones of the display substrates in the firstpass or the remaining ones of the display substrates during the secondpass.

The at least one display substrate may be separately disposed on asubstrate mounting surface of the digital imaging system and receivingthe orientation information may involve generating the orientationinformation by locating indicia on each of the display substrates.

The method may involve causing selected pixels on the at least onedisplay substrate to be actuated to display the indicia.

The at least one display substrate may include a plurality of displaysubstrates having at least one common substrate layer and receiving theorientation information may involve generating the orientationinformation by locating indicia on the at least one common substratelayer.

Locating the indicia may involve causing a camera associated with thedigital imaging system to be positioned to capture image datarepresenting a portion of the at least one display substrate bearing theindicia and the method may further involve processing the image data todetermine a relative location of the indicia.

The deposition locations may include first deposition locationsgenerally aligned along a first axis of the display substrates andsecond deposition locations generally aligned along a second axis of thedisplay substrates, and controlling the digital imaging system mayinvolve alternating between causing relative displacements in a firstpass in a first direction aligned with the second axis and a second passin a direction opposite to the first direction, and causing depositionof the filter material at a first plurality of the selected depositionlocations during the first pass, and causing deposition of the filtermaterial at a second plurality of the selected deposition locationsduring the second pass.

The first plurality of the selected deposition locations may includealternate selected deposition locations along the first axis and thesecond plurality of the selected deposition locations may includeremaining selected deposition locations along the first axis.

The method may involve displacing the digital imaging system between thefirst pass and the second pass in a direction of the first axis.

In accordance with another aspect of the invention there is provided acomputer readable medium encoded with codes for directing a controllerprocessor circuit to carry out any of the methods above.

In accordance with another aspect of the invention there is provided adisplay apparatus having filter elements formed in accordance with anyof the methods above.

In accordance with another aspect of the invention there is provided adigital imaging system operable to selectively deposit filter materialat a plurality of deposition locations to form filter elements on atleast one display substrate. The digital imaging system includes acontroller operably configured to receive orientation informationdefining a disposition of a plurality of pixels associated with the atleast one display substrate, identify pixels in the plurality of pixelsthat are to receive filter material for forming a filter element on thepixel, select deposition locations within each of the identified pixelsin accordance with the orientation information to meet an alignmentcriterion associated with placement of the filter element within thepixel, and control the digital imaging system to cause deposition of thefilter material at the selected deposition locations.

In accordance with another aspect of the invention there is provided amethod and system for forming filter elements on at least two displaysubstrates using a digital imaging system operable to selectivelydeposit filter material at a plurality of deposition locations. Thedeposition locations include first deposition locations generallyaligned along a first axis of the display substrates and seconddeposition locations generally aligned along a second axis of thedisplay substrates, the least two display substrates being disposed insuccession along the second axis. The method involves receivingorientation information defining a disposition of a plurality of pixelsassociated with each of the display substrates with respect to the firstand second axes, identifying pixels in the plurality of pixels that areto receive filter material for forming a filter element on the pixel,selecting deposition locations within each of the identified pixels inaccordance with the orientation information to meet an alignmentcriterion associated with placement of the filter element within thepixel, and computing an offset associated with the plurality of pixelsin a direction of the first axis for at least one of the displaysubstrates. The method also involves determining a residual portion ofthe offset that cannot be compensated by the selection of the depositionlocations, controlling the digital imaging system to cause deposition ofthe filter material at the selected deposition locations by causingrespective relative displacements between the display substrates and thedigital imaging system in a first pass in a first direction aligned withthe second axis and a second pass in a second direction opposite to thefirst direction, and causing deposition of filter material on alternateones of the at least two display substrates during the first pass andcausing deposition of filter material on remaining ones of the at leasttwo display substrates on the second pass. The method further involvescausing the digital imaging system to be repositioned relative to thedisplay substrates by the residual portion of the offset while disposedbetween at least one of the alternate ones of the display substrates inthe first pass or the remaining ones of the display substrates duringthe second pass.

In accordance with another aspect of the invention there is provided amethod and system for forming filter elements on a substrate, thesubstrate being subsequently aligned to a display substrate for forminga display. The method involves selecting locations to receive filtermaterial for forming filter elements on the substrate, introducing arandom variation in placement of the filter elements, and forming filterelements at the selected locations.

In accordance with another aspect of the invention there is provided acomputer readable medium encoded with codes for directing a controllerprocessor circuit to carry out the method above.

In accordance with another aspect of the invention there is provided adisplay apparatus having filter elements formed in accordance with themethod above.

In accordance with another aspect of the invention there is provided amethod for forming filter elements on a display substrate. The methodinvolves selectively depositing filter material to form the filterelements on a plurality of pixels associated with the display substrate,and selectively exposing the deposited filter material to thermal laserradiation to condition the deposited filter material.

Selectively depositing may involve causing filter material to betransferred from a donor to the display substrate in response toreceiving radiation from an imagewise controllable laser source andexposing the deposited filter material to thermal laser radiation mayinvolve exposing the deposited filter material to radiation by theimagewise controllable laser source.

Causing filter material to be transferred from the donor to the displaysubstrate may involve causing filter material to be transferred from thedonor to the display substrate for a plurality of donors, and exposingthe deposited filter material to thermal laser radiation may involveexposing the deposited filter material to thermal laser radiation oncompletion of transfer of material from each of the plurality of donors.

Selectively depositing filter material may involve controlling animagewise controllable laser source to cause the deposition of filtermaterial and exposing the deposited filter material to thermal laserradiation may involve exposing the display substrate to thermal laserradiation produced by the imagewise controllable laser source.

Selectively depositing filter material may involve controlling a firstimagewise controllable laser source to cause the deposition of filtermaterial and exposing the deposited filter material to thermal laserradiation may involve exposing the display substrate to thermal laserradiation produced by a second imagewise controllable laser source.

The method may involve changing an operating intensity associated withthe laser source prior to selectively exposing the deposited filtermaterial to thermal laser radiation.

Exposing the deposited filter material to thermal laser radiation mayinvolve selectively exposing portions of the display substrate havingdeposited filter material to thermal laser radiation.

The filter elements may include color filter elements.

The color filter elements may include color filter elements on areflective display substrate.

In accordance with another aspect of the invention there is provided acomputer readable medium encoded with codes for directing a controllerprocessor circuit to carry out any of the methods above.

In accordance with another aspect of the invention there is provided adisplay apparatus having filter elements formed in accordance with anyof the methods above.

In accordance with another aspect of the invention there is provided adigital imaging system for forming filter elements on a displaysubstrate. The system includes a controller operably configured to causethe digital imaging system to selectively deposit filter material toform the filter elements on a plurality of pixels associated with thedisplay substrate, and selectively expose the deposited filter materialto thermal laser radiation to condition the deposited filter material.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

FIG. 1 is a perspective view of a digital imaging system;

FIG. 2 is a plan view of a portion of a display substrate produced inthe digital imaging system shown in FIG. 1 in accordance with a firstembodiment of the invention;

FIG. 3 is a block diagram of a processor circuit embodiment of acontroller shown in FIG. 1;

FIG. 4 is a process flowchart for causing the processor circuit shown inFIG. 3 to cause filter elements to be formed on the plurality of displaysubstrates;

FIG. 5 is a process flowchart of a portion of the process shown in FIG.4 for receiving orientation information;

FIG. 6 is a plan schematic view of a plurality of display substratesshown in FIG. 1;

FIG. 7 is an enlarged view of two of the display substrates shown inFIG. 6;

FIG. 8 is a process flowchart of a portion of the process shown in FIG.4 for selecting deposition locations;

FIG. 9 is a further enlarged view of two of the display substrates shownin FIG. 6 in accordance with an alternative embodiment of the invention;

FIG. 10 is a schematic view of three of the display substrates shown inFIG. 6 in accordance with an alternative embodiment of the invention;

FIG. 11 is a schematic view of three of the display substrates shown inFIG. 6 in accordance with another alternative embodiment of theinvention;

FIG. 12 is a schematic view of one of the display substrates shown inFIG. 6 in accordance with yet another alternative embodiment of theinvention; and

FIG. 13 is a process flowchart for causing the processor circuit shownin FIG. 3 to carry out a process for conditioning deposited filterelements.

DETAILED DESCRIPTION Digital Imaging System

Referring to FIG. 1, a digital imaging system is shown generally at 100.The system 100 is configured as a flat bed imaging system and includes adimensionally stable base 102 having a flat upper surface 104.

The system 100 also includes a bridge 106, supported on the base 102.The bridge 106 provides a stable support for an imaging head 108, whichis mounted on the bridge for motion in a first axis (indicated by thearrow 110). In the embodiment shown, the system 100 includes a firstaxis linear motor 112 for moving the imaging head 108 in eitherdirection along the first axis 110. The linear motor 112 furtherincludes encoder graduations 114 that provide positional feedback, thusfacilitating precise positioning and motion control of the imaging head108.

The system 100 also includes a mounting table or chuck 116, having aflat mounting surface 118 for mounting a plurality of display substrates120. In this embodiment the chuck 116 includes a plurality of portsdistributed over the mounting surface 118, which when coupled to avacuum generator (not shown) draws the display substrates 120 into closecontact with the flat mounting surface 118. The chuck 116 is supportedon an air bearing (not shown) for reciprocating motion in a second axis(indicated by the arrow 124). In flat bed imaging systems, the secondaxis 124 is generally orthogonal to the first axis 110, although in someembodiments the angle between the first and second axes may be otherthan 90°. The system 100 further includes a second axis linear motor 122for moving the chuck 116 in either direction along the second axis 124.The linear motor 122 also includes encoder graduations 126 that providefor positional feedback and control of the reciprocating motion in thesecond axis.

In one embodiment the imaging head 108 comprises a radiation source thatis configured to provide a plurality of beams 128. The radiation sourcemay be a laser, such as a laser diode and the imaging head 108 mayfurther include a multi-channel modulator (not shown), in whichindividual channels are selectively actuated to generate the pluralityof beams 128.

While the embodiment shown in FIG. 1 has been described as includingparticular components such as the linear motors 112 and 122 the system100 could equally well be implemented using other components such as arotating motor and ball screw mechanism or a belt drive, for example.Similarly, the chuck 116 may remain stationary and motion of the imaginghead 108 may be provided by mounting the imaging head on a gantry thatpermits movement of the imaging head in both directions aligned with theaxes 110 and 124.

In the embodiment shown in FIG. 1, each of the display substrates isseparated from adjacent display substrates, and when mounted on thechuck 116 would likely have non-negligible differences in orientation,which need to be accounted for in subsequent imaging processes. In otherembodiments, single or multiple display substrates 120 may be processedon a single substrate or other carrier which is loaded into the digitalimaging system 100 as a single substrate. In such embodiments theregistration between display substrates 120 may be significantly moreprecise.

Each of the display substrates 120 includes a plurality of indicia 134disposed on an exposed outer surface 130 of the display substrate forfacilitating generation of orientation information associated with therelative placement of the display substrates. The system 100 furtherincludes a camera 132 mounted on the imaging head 108, which isconfigured to capture images of the indicia for generating theorientation information. Since the camera 132 is mounted to the imaginghead 108 and therefore moves with the imaging head, the precisepositioning of the camera is also provided by the encoder graduations114 associated with the linear motor 112. Images of the indicia 134captured by the camera 132 may thus be processed to determine a relativeorientation of each of the display substrates 120. A relativeorientation between the plurality of imaging beams 128 and the camera132 may be determined by using one or more imaging beams 128 to producea target feature on a test surface mounted on the chuck 116. Images ofthis target feature may then be captured and processed to determine arelative offset between the imaging beams 128 and the camera 132, whichmay be saved as a calibration value.

In the embodiment shown the display substrates 120 each include threeindicia 134 that may have been marked on the display substrates in aprevious processing step. Alternatively, in some embodiments where thedisplay substrates 120 comprise reflective display pixels that arealready operable, selected pixels on each display substrate may beactuated to display the indicia, thus removing the need for the displaysubstrates to include previously marked indica. In other embodiments,the indica may comprise physical features of the display substrate, suchas a portion of a TFT element associated with particular pixels, forexample. In each of these indicia embodiments, the indicia on thedisplay substrates 120 are disposed in a known fixed relation to thedisplay pixels 200 and thus, together with a knowledge of the pixel sizeand configuration provides a relative location of each pixel withrespect to the indicia. In general, pixels 200 of the display substratesare formed in a lithographic process which provides very preciselyspaced and oriented pixels 200 and indicia 134.

In some embodiments, it may be necessary to provide for motion in athird axis that is generally orthogonal to the first and second axes 110and 124 to account for differences in thickness between various displaysubstrates that may be processed using the system 100. For an imaginghead 108 that uses high numerical aperture imaging optics for formingthe plurality of imaging beams 128, it may be necessary for the imaginghead to employ an auto-focus system for maintaining focus of the beamsover a full imaging area of the system 100. In such cases adjustment inthe third axis may be important for ensuring that the auto-focus systemis able to maintain focus.

In one embodiment filter material for forming filter elements on theplurality of display substrates 120 is provided in the form of a donorsheet 150 (a portion of which is shown in FIG. 1). The donor sheet 150includes filter material disposed on a support layer such as a polyesterfilm. The donor 150 may also include a release layer disposed betweenthe filter material and support layer for enhancing transfer of filtermaterial to the display substrates when exposed to radiation from thebeams 128. For forming color filter elements, the filter material maycomprise a plurality of colorants such as red, green, and bluecolorants, or cyan, magenta, and yellow colorants, for example. Othercolorants may also be added to the plurality of colorants. For example,a colorant such as a yellow colorant may be added to red, green and bluecolorants to enhance a color gamut of the display. In such casesdifferent donors 150 would be separately mounted and imaged to completethe color filter element deposition process. Thermal transfer donortechnology is used commercially in the graphic arts industry, andseveral donor media such as Fuji Finalproof® and Kodak Approval™ areavailable for producing color proofs of digital images. A suitable donor150 would thus include colorant material that is tailored to providecolor filter elements having a desired light transmissioncharacteristic.

While the embodiments herein are generally described with reference todeposition of color filter elements that are configured to transmitspecific incident light wavelengths, the filter element may equally wellinteract to alter other properties of incident light. For example, thefilter elements may comprise polarizing material that is deposited onselected pixels to polarize light transmitted through the filterelement. Other examples of filter elements that may be deposited includeinterference filters or anti-glare filters.

As noted above, in the embodiment shown in FIG. 1 the imaging head 108is a multi-channel imaging head that produces a plurality of imagingbeams 128, which are directed toward the donor sheet 150 covering theexposed outer surface 130 of the display substrates 120. The donor 150may be applied by rolling donor material into close contact with thedisplay substrates 120 and secured in place by vacuum applied to theplurality of ports distributed over the mounting surface 118. Theplurality of ports on the mounting surface 118 may be divided intosubstrate port regions and donor port regions that are in communicationwith separate vacuum circuits to permit the display substrates 120 to besecured in place while the donor 150 is applied. The donor region portswould then be activated to secure the donor in place during or afterbeing rolled into contact with the plurality of display substrates 120.

The system 100 further includes a controller 140, which is operablyconfigured to control operations of the digital imaging system. Thecontroller 140 includes control signal input/output ports 142, 144, and146 for controlling the imaging head 108, linear motor 112, and linearmotor 122 respectively. Other signal outputs (not shown) may be providedfor controlling the vacuum generator, donor mounting and other imagingsystem functions as necessary. In the embodiment shown, the signal port142 produces signals for controlling the imaging head 108 to modulateselected ones of the plurality of imaging beams 128 in accordance withimage data that is stored within the controller. The image data may bestored in the form of an image file such as a tagged image format (TIFF)file, for example.

Imaging of the thermal transfer donor may require that the imaging head108 be configured to produce infra-red light having a wavelength andpower that is sufficient to cause thermal transfer of colorant from thedonor 150 onto the display substrates 120. One suitable imaging head 108is the Thermal SQUAREspot® imaging head produced by the Eastman KodakCompany of Rochester, N.Y. While the various embodiments of theinvention disclosed herein are described with reference to imaging of athermal transfer donor, other imaging techniques for transfer of filtermaterial such as inkjet transfer, UV transfer, laser exposure of a colorresist material, or other methods may equally well be implemented toform filter elements on the display substrates 120.

In operation of the system 100, the controller 140 causes the chuck 116to move along the second axis 124, while the imaging head 108 modulatesthe plurality of imaging beams 128 in accordance with the image datareceived from the signal port 142 of the controller 140. In oneembodiment, the chuck 116 is traversed at a velocity of about 2 m/s. Theresulting relative motion between the chuck 116 and imaging head 108causes the plurality of imaging beams 128 to image a swath (shown inbroken outline at 136) along the second axis having a width thatcorresponds in width to the number of beams 128 generated by the imaginghead 108. In one embodiment the imaging head 108 generates 224 imagingbeams that are spaced apart by 10.6 μm thus providing a swath width of2.374 mm.

Once the chuck 116 has traversed the plurality of display substrates 120in a first pass, the controller 140 causes the linear motor 122 todecelerate the chuck 116 to a stop and to reverse the traversingdirection of the chuck. While the chuck 116 is being decelerated, thelinear motor 112 shifts the imaging head 108 over by a swath width (i.e.by 2.374 mm in the above example) and imaging of a further swath (notshown in FIG. 1) adjacent to the swath 136 commences on the returntraverse of the chuck 116 in a second pass over the substrates 120.Accordingly, in this described operational embodiment, a swath is imagedfor each pass of the chuck 116. In other embodiments however, it may bedesirable to image in an interleaved manner as described later herein.In such cases, the linear motor 112 may shift the imaging head 108 overby less than a swath width such that the next imaging swath at leastpartly overlaps the already imaged swath.

The traversal of the chuck 116 and shifting of the imaging head 108 toimage successive swaths across the plurality of display substrates 120facilitates deposition of filter material at a plurality of depositionlocations. For an imaging head 108 having a plurality of imaging beams128 that have a fixed spacing between beams, corresponding depositionlocations are defined in the direction of the first axis 110 at aplurality of discrete locations. However, in the exposure headembodiment described above, the beams 128 are traversed across thedisplay substrates 120 in the direction of the second axis 124 andaccordingly deposition in this axis may occur over a greater or lesserarea than provided in the direction of the first axis 110. In theexample of the Kodak SQUARESpot® imaging head, the beams 128 may have agenerally rectangular profile extending to approximately 10.6 μm in thefirst axis direction 110, and only about 1-2 μm in the second axisdirection 124. In this case, the deposition locations in the second axisdirection 124 may be controlled to deposit filter material with greaterprecision than is possible in the first axis direction 110.

In the embodiment shown in FIG. 1, the chuck 116 traverses across theupper surface 104 of the base 102 in the direction of the second axis124, while the imaging head 108 only moves in the direction of the firstaxis 110. In other embodiments, the chuck may be stationary with respectto the base 102 and the bridge 106 may be disposed on a linear track forproviding a traversing motion of the imaging head 108 in both the firstand second axes 110 and 124.

In many cases the display substrates 120 on which filter elements are tobe formed are rigid. However, even when the display being produced is tobe a flexible display, it is quite common to process such a flexibledisplay while mounted to a rigid carrier that is later removed. In otherembodiments flexible display substrates may be configured so as to besuitable for mounting on a cylindrical drum surface, in which case adrum-based imager may be substituted for the flat bed imager shown inFIG. 1. The flat-bed imaging system shown in FIG. 1 may also be used toprocess flexible substrates.

Display Substrate

A display substrate portion 138 (shown in FIG. 1) of one of the displaysubstrates 120 is shown in greater detail in FIG. 2. Referring to FIG.2, the display substrate portion 138 includes a plurality of pixels 200,which in this embodiment are reflective display pixels in that ambientlight incident on the pixel changes state from being reflected by thepixel to being absorbed by the pixel in response to a actuation signalbeing provided to an underlying driver (not shown).

In the specific embodiment shown, the pixels 200 include a firstplurality of pixels that have a green color filter element 202 formed onthe pixel, a second plurality of pixels that have a blue color filterelement 204 formed on the pixel, and a third plurality of pixels thathave a red color filter element 206 formed on the pixel. A furtherfourth plurality of uncovered pixels 208 do not have any color filterelement formed on the pixel. The color filter elements 202-206 anduncovered pixels 208 are operable to produce a reflected image, in whichlight reflected from the first, second and third plurality of pixelsprovide a color component to the resultant image, while the uncoveredpixels 208 provide for a brighter display. As such, a tradeoff of suchan arrangement is between a reduced color gamut and brightness of thedisplayed image due to the inclusion of uncovered pixels 208. In theembodiment shown, each colored filter element 202-206 covers only aportion of an area associated with the each covered pixel 200, while aportion 210 of the area remains uncovered. The uncovered areas 210 havethe same function as the uncovered pixels 208, in that these uncoveredareas enhance the brightness of the reflective display. The uncoveredareas 210 also permit tolerances associated with placement of the filterelements 202-206 to be relaxed, since these uncovered areas reduce thepossibility of filter element material deposition extending beyondextents of the associated pixels 200 into neighboring pixels. Variousother arrangements of color filter elements 202-206, uncovered pixels208, and uncovered areas 210 may be used to produce the reflectivedisplay. For example, some embodiments may omit the uncovered pixels 208in favor of an increased uncovered area 210. Likewise, other embodimentsmay substantially cover the area of each pixel with filter material, andrely on uncovered pixels 208 to generate the required displaybrightness.

While color filters for reflective displays can be produced on aseparate substrate as in the case of transmissive displays, the colorfilter elements may also be formed directly on the reflective displaypixels using digital imaging techniques. Digital imaging of colorfilters involves selectively transferring colorant onto an otherwisemonochromatic reflective display using a digital imaging system.

Non-reflective displays, such as LCD displays generally require that anentire light generating area of the pixel be covered by filter material,however non-light generating areas of the pixel are often covered by ablack matrix material that masks these areas. In such displays thatgenerate a luminous flux within the display itself, brightness may beincreased by increasing back-illumination intensity and thus displaybrightness may be less of a concern than for reflective displays.Regardless of the type of display, filter element placement should besufficiently precise to avoid undesirable effects, such as partialcoverage of a neighboring pixel by an adjacent filter element or failureto cover a sufficient area of the pixel. Lack of placement accuracy mayalso cause undesirable image artifacts that are visible to the eye anddetract from the quality of the image produced by the resulting display.In particular, the human eye is very sensitive to repeating patterns,which may be caused by color filter element placement errors.

In one embodiment, the pixels 200 on a reflective display may havedimensions of between about 90 μm and about 220 μm, and a coverage areaof the color filter material may be in the region of about 60% to about100% of the pixel area.

When imaging multiple display substrates 120, throughput is an importantconsideration and it is desirable to process multiple displays as shownin FIG. 1. Simultaneous imaging of multiple display substrates 120reduces the time overhead associated with loading and unloading ofdisplay substrates 120 and the associated donor sheets 150. Simultaneousimaging also reduces overhead associated with decelerating the chuck 116at the end of each traverse, reversing the direction of chuck movement,and accelerating up to imaging speed again when compared to imaging of asingle display substrate at a time.

In embodiments where the plurality of display substrates 120 remainconnected via a common carrier or substrate layer, the offset androtation of pixels of each of the display substrates should besubstantially aligned. However, in other embodiments, such as shown inFIG. 1, each of the display substrates 120, even if initially processedas part of a larger substrate bearing multiple displays, have beenseparated and may thus have non-negligible differences in orientationbetween respective displays that complicate alignment of the imagingaxis to suit pixel orientation, since pixels on one display substrateare not necessarily aligned with pixels on other display substrates.

Accordingly, it will generally not be possible to select an image startposition that guarantees correct placement of filter elements 202-206 onall of the plurality of display substrates. This error may besignificant depending on the relative alignment between each of thesubstrates and failure to account for such differences may result insignificant placement errors of the filter elements with respect to thepixels of the display substrate. Furthermore the display substrates 120may also be rotated with respect to the axes 110 and 124, which wouldintroduce additional placement errors.

Digital Imaging System Controller

Referring to FIG. 3, in one embodiment the controller 140 may beimplemented using a processor circuit shown generally at 300. Theprocessor circuit 300 includes a microprocessor 302, a program memory304, a variable memory 306, a media reader 308, and an input output port(I/O) 310, all of which are in communication with the microprocessor302.

Program codes for directing the microprocessor 302 to carry out variousfunctions are stored in the program memory 304, which may be implementedas a random access memory (RAM), a hard disk drive (HDD), a non-volatilememory such as flash, or a combination thereof. The program memoryincludes a first block of program codes 320 for directing themicroprocessor 302 to perform operating system functions and a secondblock of codes 322 for directing the microprocessor to control imagingfunctions of the digital imaging system 100 to form filter elements onthe plurality of display substrates 120.

The media reader 308 facilitates loading program codes into the programmemory 304 from a computer readable medium 312, such as a CD ROM disk314, flash memory 316, or a computer readable signal 318 such as may bereceived over a network, for example.

The I/O 310 includes the control signal input/output port 142. The I/O310 also includes a motor driver 380 having a control port 144 forcontrolling the first axis linear motor 112 and a motor driver 382having a control port 146 for controlling the second axis linear motor122. The I/O 310 may additionally include other outputs and/or inputsfor controlling other functions of the digital imaging system 100, suchas operation of the camera 132, loading of the donor 150, vacuumoperations of the chuck 116, etc.

The variable memory 306 includes a plurality of storage locationsincluding a orientation information store 350 for storing displaysubstrate and pixel values, a display configuration store 352 forstoring values associated with the pixel configuration associated withthe display substrates 120, a store 354 for storing a placementthreshold value, and a digital mask store 356 for storing depositionlocation mask values. The variable memory 306 may be implemented inrandom access memory, a flash memory, or a hard drive, for example.

In other embodiments (not shown), the controller 140 may be partly orfully implemented using a hardware logic circuit including discretelogic circuits and/or an application specific integrated circuit (ASIC),for example.

Forming Filter Elements

Referring to FIG. 4, a flowchart depicting blocks of code for directingthe processor circuit 300 to cause filter elements to be formed on theplurality of display substrates 120 using the digital imaging system 100is shown generally at 400. The blocks generally represent codes that maybe read from the computer readable medium 312, and stored in the programmemory store 322, for directing the microprocessor 302 to performvarious functions related to depositing filter element material on thedisplays 120. The actual code to implement each block may be written inany suitable program language, such as C, C++ and/or assembly code, forexample.

The process 400 begins at block 402, which directs the microprocessor302 to receive orientation information defining a disposition of theplurality of pixels 200 associated with each of the display substrates120.

The process then continues at block 404, which directs themicroprocessor 302 to identify pixels in the plurality of pixels 200that are to receive filter material for forming filter elements 202-206on the identified pixels. In one embodiment, block 404 directs themicroprocessor 302 to read pixel configuration information from thedisplay configuration store 352 of the variable memory 306. In manyembodiments the display substrates 120 would be identically configuredand the pixel configuration (i.e. the size, number, and layout of thepixels) would that be the same. In other embodiments, differentconfigurations of display substrates 120 may be processed at the sametime and in such cases pixel configuration information would be readfrom the display configuration store 352 for each of the displaysubstrates 120. The pixel configuration information read from the store352 identifies which of the pixels (i.e. the groups of pixels in FIG. 2on which the filter elements 202-206 are disposed) are to receiverespective color filter material, and may further define the size of thefilter elements and/or the uncovered areas 210. The pixel configurationinformation may be stored as a file including coordinates identifyingthe pixels, for example.

Block 406 then directs the microprocessor 302 to select depositionlocations within each of the identified pixels in accordance with theorientation information received at block 402. In one embodiment thedeposition locations are selected to meet an alignment criterionassociated with placement of the filter elements 202-206 within thepixels 200, as described in more detail later herein. Block 408 mayfurther direct the microprocessor 302 to save digital mask valuesidentifying the selected deposition locations for each filter element inthe digital mask store 356 of the variable memory 306. The digital maskmay be stored as an image file such as a bitmap file, TIFF file, orother suitable file format.

The process 400 then continues at block 408, which directs themicroprocessor 302 to read the digital mask values in the digital maskstore 356 and to generate control signals at the ports 142, 144, and 146to cause deposition of the filter material at the selected depositionlocations, as described above in connection with the digital imagingsystem 100. The imaging head 108 responds by actuating the laser beam orbeams that correspond to the selected deposition locations.

In the process embodiment 400 shown in FIG. 4, blocks 404 and 406 may becompleted prior to commencing deposition of the filter element materialat block 408. However in other embodiments block 408 may start beforeblock 404 and/or 406 have completed.

Receiving Orientation Information

The process of block 402 shown in FIG. 4 for receiving orientationinformation is shown in greater detail at 402 in FIG. 5. Referring toFIG. 5, the process 402 is executed for each display substrate in theplurality of display substrates 120. The process begins at block 500,which directs the microprocessor 302 to generate control signals tocause the camera 132 to be positioned to capture image data representingportions of the each of the display substrates 120 bearing the indicia134.

The display substrates 120 are shown in plan schematic view in FIG. 6.Referring to FIG. 6, in one embodiment nine separate display substratesare mounted for simultaneous processing in the digital imaging system100. In general the display substrates 120 would be mounted in a frame(not shown in FIG. 1) that would orient each display approximatelyorthogonally with respect to the first and second axes 110 and 124defined in the direction of the motions of the imaging head 108 andchuck 116. In FIG. 6, the frame is represented by broken lines 608-612and 614-618, which represent a desired disposition of the plurality ofdisplay substrates 120 with respect to the axes 110 and 124.

In general, the display pixels 200 on the display substrates 120 may beformed by a lithographic process, which provides precisely spaced andoriented pixels 200. However subsequent dicing to separate the displaysubstrates into individual display substrates 120 may result in thepixels 200 being slightly misaligned with respect to edges of thesubstrate. Registration to the frame, if provided, may also be imprecisewhen compared to dimensions of the pixels and/or the spacing betweendeposition locations provided by the imaging head 108. Accordingly, asecond display substrate 604 of the plurality of display substrates 120has an associated disposition with respect to the axes 110 and 124 thatincludes an offset D₁ with respect to the line 614, an offset D₂ withrespect to the line 610, and a rotation angle θ. In FIG. 6, suchmisalignments have been exaggerated for sake of clarity, as have thesize of the pixels 200. In practice, misalignments may be small enoughto be unnoticeable to the naked eye, but large enough to cause at leastsome placement inaccuracy of the filter elements 202-206 if notcorrected. Furthermore, in a practiced display the pixels wouldgenerally be significantly smaller and greater in number than show inFIG. 6.

The process then continues at block 502, which directs themicroprocessor to process the images to determine coordinates (x₁,y₁),(x₂,y₂) and (x₃,y₃) of each of the indicia 134 on the display. As anexample, the coordinates (x₁,y₁) for the first upper right hand indicia134 for a first display substrate 602 of the plurality of displaysubstrates 120 are shown as being referenced to the coordinate framedefined by axes 110 and 124.

Block 504 then directs the microprocessor 302 to compute values for D₁,D₂, and θ for the display substrate and block 506 directs themicroprocessor to store the values in the orientation information store350 of the variable memory 306 (shown in FIG. 3). Referring to FIG. 6,in this embodiment the value of D₁ is calculated as an offset from theline 614 to the first indicia on each display substrate, as shown inconnection with the display substrate 604. Similarly the value of D₂ iscalculated as an offset from the line 610 to the first indicia. In thisembodiment the angle θ for each display substrate is defined as theangular deviation of a line extending between the upper and lower righthand indicia on the display substrate 604 with respect to the secondaxis 124. The angle θ is thus given by:

$\begin{matrix}{\theta = {\arctan \left\lbrack \frac{x_{2} - x_{1}}{y_{2} - y_{1}} \right\rbrack}} & {{Eqn}\mspace{14mu} 1}\end{matrix}$

where (x₁,y₁), (x₂,y₂) are the respective coordinates of the upper andlower right hand indicia as determined in block 502. Block 506 thendirects the microprocessor 302 to store the values in the orientationinformation store 350 of the variable memory 306.

Selecting Deposition Locations

Following execution of blocks 402 and 404 of the process 400, theinformation stored in the orientation information store 350 and displayconfiguration store 352 of the variable memory 306 facilitatescalculation of a disposition of the plurality of pixels 200 associatedwith each of the display substrates 120 with respect to the first andsecond axes 110 and 124. Two of the display substrates 602 and 604 areshown in enlarged view in FIG. 7. Referring to FIG. 7, the imaging swath136 produced by the imaging head 108 is shown superimposed over thedisplay substrates 602-604, and includes a plurality of depositionlocations 700. In the depicted embodiment, the imaging head 108 isconfigured to produce 24 deposition locations in the direction of thesecond axis. The deposition locations 700 in FIG. 7 are shown as havingsimilar width in the first axis 110 and length along the second axis124, however in other embodiments, the first axis width and second axislength may not be the same. Since the movement of the imaging head 108and chuck 116 define the first and second axes 110 and 124, the swath136 is aligned with the first and second axes.

A first embodiment of the process of block 406 (shown in FIG. 4) forselecting deposition locations along the first axis 110 is shown at 800in FIG. 8. Referring to FIG. 8, the process 800 begins at block 802,which directs the microprocessor 302 to read a placement threshold valuefrom the threshold value store 354 of the variable memory 306. Theplacement threshold value represents a permitted deviation in placementof filter elements with respect to extents of the identified pixels 200.Block 804 then directs the microprocessor 302 to read the configurationinformation for the display substrate 602 from the store 352. Block 804also directs the microprocessor 302 to read the orientation informationfor the display substrate 602 from the store 350.

The process 800 then continues at block 806, which directs themicroprocessor 302 to use the configuration information and orientationinformation to determine the disposition of the extents of a firstidentified pixel 702 with respect to the deposition locations 700. Theorientation information provides values for D₁, D₂, and θ that, togetherwith the pixel configuration for the display substrate permit thelocation and extents of each pixel on the display substrate to becomputed with respect to the first and second axes 110 and 124.

Block 808 then directs the microprocessor 302 to select depositionlocations that would cause placement of a first filter element 710 in agenerally centered location within the pixel extents. Referring back toFIG. 7, the first filter element 710 is shown to cover 16 depositionlocations and is generally spaced inwardly by about one depositionlocation from the pixel extents along the first axis 110. Block 808further directs the microprocessor 302 to save the selected depositionlocations for the first filter element 710 in the digital mask store 356of the variable memory 306.

The process 800 then continues at block 810, which directs themicroprocessor 302 to process the next identified pixel 704 along thesecond axis 124 by calculating placement of the second filter element712 for the same first axis deposition locations as the first filterelement 710. In the embodiment shown, a placement deviation value withrespect to the center of the extents of the second pixel 704 iscalculated for the filter element 712.

Block 812 then directs the microprocessor 302 to determine whether theplacement deviation of the second filter element 712 meets the alignmentcriterion, which in this case involves determining whether the deviationvalue is less than or equal to the threshold value read at block 802. Ifat block 812 the alignment criterion is met then the process continuesat block 814, which directs the microprocessor 302 to save the selecteddeposition locations for the second filter element 712 in the digitalmask store 356. The process then continues at block 816, which directsthe microprocessor 302 to determine whether all filter elements for thesubstrate 602 have been placed. In this case, since further filterelements 714 and 718 are still to be placed, block 816 directs themicroprocessor 302 back to block 810 and the third pixel 706 isprocessed in a similar manner.

In the example shown in FIG. 7, the third pixel 706 also meets thealignment criteria and digital mask values identifying the selecteddeposition locations are thus saved to the digital mask in the store356. Filter element placement on the display substrate 602 for the firstthree filter elements 710-714 thus shifts sequentially toward the leftin the direction of the first axis 110, while the alignment criterion ofblock 812 is met.

If at block 812 the alignment criterion is not met then the processcontinues at block 818, which directs the microprocessor 302 to shiftthe filter element placement by one of more deposition locations alongthe first axis 110 to generally re-center the filter element within thepixel along the first axis 110. Referring back to FIG. 7, in the exampleshown the alignment criteria at block 812 was not met for the fourthpixel 708, and accordingly placement of the fourth filter element 716 isshown shifted back along the first axis by one first axis depositionlocation. The process 800 then continues at block 818, which directs themicroprocessor 302 to block 816, which directs the microprocessor tosave the selected deposition locations for the fourth filter element 716in the digital mask store 356.

In the embodiment shown in FIG. 7, the 24 deposition locations providedby the imaging head 108 permit two columns of filter elements to besimultaneously deposited and the process 800 may thus be executed togenerate digital mask values for placement of additional elements718-722 within the imaging swath 136. Similarly, the process 800 wouldbe executed for subsequent swaths (not shown) along the first axis 110to provide digital mask values covering all of the pixels 200 associatedwith the display substrate. In the example shown in FIG. 7, the filterelements 710-722 correspond to the green filter elements 202 shown inFIG. 2, and deposition locations of further filter elements 204 and 206may be similarly selected by executing the same process 800.

If at block 816, all filter elements for the display substrate 602 havebeen placed, then block 816 directs the microprocessor 302 to block 820which directs the microprocessor 302 to process the next displaysubstrate, which in this case is the display substrate 604. Block 820then directs the microprocessor 302 back to block 804 where displayconfiguration information and orientation information for the nextsubstrate 604 is read. In embodiments where all of the substrates 120have identical configurations, the step of reading the configurationinformation may be omitted. Block 806 again directs the microprocessor302 to use the configuration information and orientation information todetermine the disposition of the extents of a first identified pixel 702with respect to the deposition locations 700. As for the substrate 602,the orientation information provides values for D₁, D₂, and θ thatpermit the location and extents of each pixel on the display substrateto be computed with respect to the first and second axes 110 and 124.Referring to FIG. 7, a first identified pixel 726 on the displaysubstrate 604 that is to receive deposition of a filter element 728 isfurther offset to the left along the first axis 110. In this case thefilter element 728 is offset as indicated at 730 from the beginning ofthe swath 136, and this offset is greater than the offset 732 associatedwith the first filter element 710 on the display substrate 602. Theprocess 800 thus takes account of the differences in relativeorientation between the display substrates 602 and 604 through selectionof deposition locations. Once all substrates in the plurality of displaysubstrates 120 have been processed, the process 800 is terminated.

Due to differences in the orientation of the display substrates 602 and604, selection of the deposition locations 700 that are to be actuatedfor each identified pixel 702-708 results in a successive variation ofthe placement of the color filter elements 710-716 within the pixels.

In one embodiment, the threshold value that is stored in the store 354may be pre-determined based on the respective sizes of the pixels702-708 and the desired coverage of the filter elements 710-722. For theexample of a spacing between deposition locations of 10.6 μm, a pixelextent in the first axis direction of 70 um, and a 60% coverage of thepixel by the filter element, the threshold may be set at a value ofabout 5 μm. Accordingly, once the deviation of the filter element fromcenter reaches 5 μm, the filter element is moved along the axis backtoward the center of the pixel by 10.6 μm. In other embodiments thespacing between deposition locations, pixel extent, and/or coverage ofthe pixel by the filter element may be less than or greater than thevalues above and the threshold may be selected accordingly. For example,in reference to FIG. 2, the threshold may be selected as a proportion ofthe uncovered areas 210 of the pixels 200. In one embodiment, thethreshold value may be selected by assigning an initial threshold,processing one or more display substrates using the selected initialthreshold, and then examining the resulting display for image artifactsor other defects. The process may then be repeated using differentthreshold values until a desired result is obtained.

In the embodiment shown in FIG. 7, deposition locations along the secondaxis 124 have the same spacing as the spacing between depositionlocations along the first axis 110 and a similar process to the process800 may thus be implemented to select deposition locations along thesecond axis. In other embodiments, the second axis deposition locationsmay be more closely spaced than the first axis deposition locations

Referring back to FIG. 2, in the display substrate example shown bluecolor filter elements 204 are disposed adjacent to the green colorfilter elements 202. Execution of the process 800 may result in thefilter elements 204 having the same successive shifts and thus acorresponding regular placement pattern and such a pattern may reinforcethe pattern already present in the placement of the filter elements 202.Accordingly in a second embodiment, the process 800 may be implementedto cause placement of the filter elements 204 to be varied between eachof the plurality of colored filter materials to disrupt reinforcement ofany regular patterns that occur. Such a variation may also in somecircumstances lessen the effect of the pattern associated with the colorfilter elements 202, since an overall pattern frequency may be increasedthus reducing the ability of the user's eye to discern the resultingpattern. Such variation may be introduced by deliberately offsettingcertain filter elements from the generally centered location within thepixel extents such that the successive shifts cause an offset pattern inthe placement of the filter elements 204. Similar offsets may also beapplied to the placement of the red color filter elements 206.

In a third embodiment of the process of block 406 shown in FIG. 4, anadditional step may be added to the process 800 to introduce a randomvariation in the threshold value read at block 802. For somecombinations of pixel size, filter element coverage, and/or depositionlocation spacing, the sequential shifting of filter element placementthat would occur when implementing the process 800 shown in FIG. 8 wouldlead to regular patterns in filter element placement, to which the humaneye is very sensitive as disclosed earlier herein. The random variationin threshold value would act to disrupt the regular patterns that occurin filter element placement due to the sequentially shifted placement ofthe filter elements and associated shifts that occur in implementing theprocess 800. In one embodiment the random variation may be set as aproportion of the threshold value, for example ±40% or ±2 μm for thecase of a 5 μm threshold value, which would thus cause the placementthreshold value to be randomly selected from a set of threshold valuesincluding 3 μm, 5 μm, and 7 μm. Such random selection from the set ofthreshold values may be done on the basis of a random number provided bya random number generator associated with the operating systemimplemented by the operating system codes in the first block of programcodes 320 of the program memory 304 shown in FIG. 3.

The second and third embodiments as described above may also be appliedin combination, thereby offsetting patterns for the different colorfilter elements 202-206 while also introducing random variations inplacement of the filter elements to additionally disrupt placementpatters that may occur. Alternatively, identifying the pixels to receivefilter material at block 404 of the process 400 shown in FIG. 4 mayinvolve randomly identifying pixels in the plurality of pixels 200 toreceive one of the plurality of colored filter materials. In thisembodiment the resulting filter elements of each color would be randomlydispersed across each display substrate, thus disrupting patterns thatmay occur due to filter element placement. The randomized filter elementlocations would need to be provided to a display driver associated withthe display substrate such that correct pixels may be actuated for eachof the corresponding color filter elements.

While in this embodiment random variations in placement of the filterelements is accomplished by introducing a random variation in thethreshold read at block 802, in other embodiments such random placementvariation may be introduced elsewhere in the process 800. For example,block 808 may direct the microprocessor 302 to introduce randomnessindependent of the threshold value. Other implementations andembodiments described herein may also introduce a random placementvariation to disrupt regular patterns that occur in filter elementplacement in said indentified pixels on each display substrate.

Similarly, in embodiments where filter elements are to be formed on aglass substrate or other substrate such as plastic that is subsequentlyaligned to the display substrate, the color filter elements may beformed using the system 100 shown in FIG. 1, or may be formed using analternative processes for forming filter elements, such asphotolithography, for example. In a further processing step, theintroduction of random variations in filter element placement describedherein may be implemented to disrupt regular patterns that may occuronce the filter elements formed on the glass substrate have been alignedto the display. Such patterns may occur due to mis-alignment between thefilter element substrate and the underlying pixels of the display. Therandom variation may be operable to disrupt patterns caused fromalignment shifts between the color filter elements and the displaypixels when the glass color filter is placed on top of the display. Suchpatterns may result from aliasing between the two patterns of thedisplay pixels and filter elements as manifested when the color filtersubstrate and display substrate are attached to each other. The randomvariation may help to reduce such patterns and relax alignment precisionrequirements.

Repositioning of the Digital Imaging System

In the process 800 described above, when commencing processing of thefirst display substrate 602, the imaging head 108 may be positionedalong the first axis in accordance with the orientation information readat block 804 such that the swath 136 is aligned for deposition of filterelement material on the pixels 702-708 and other pixels on the displaysubstrate. Such alignments may be made within the precision provided bythe first axis linear motor 112 and associated encoder graduations 114.In one embodiment, placement accuracy may be about ±3 μm and the encoderresolution may be less than ±1 μm. Accordingly, block 808 may includethe additional step of determining and applying such an alignment.However, when processing subsequent display substrates that are notprecisely aligned to the display substrate 602, such as the displaysubstrate 604 shown in FIG. 7, the swath may not be optimally aligned tothe pixels of the second substrate. While the offset 730 is able tocorrect for some of the difference in alignment between substrates 602and 604, there would remain a residual offset of at least half of aspacing between adjacent deposition locations.

Referring to FIG. 9, in an alternative embodiment of the process 800shown in FIG. 7, the imaging head 108 may be repositioned afterdeposition of the filter elements on the substrate 602 by causing asmall displacement 900 in the direction of the first axis 110 thatcorresponds to the residual offset. During deposition of the filterelements, the exposure head 108 is displaced relative to the substratesin the direction of the second axis 124, and repositioning of theimaging head 108 to account for the residual offset that would be causedby the imaging swath 136, results in an offset imaging swath 902. Theimaging swath 902 is thus offset by less than or equal to half of aspacing between adjacent deposition locations and aligns with the pixel726 of the display substrate 604.

In order to increase filter element deposition speed in the digitalimaging system 100, velocities in the second axis direction may be inthe region of about 2 m/s or greater. For a 20 mm spacing betweendisplay substrates 602 and 604 the time that would be available for thedisplacement would be in the region of 10 milliseconds, thus requiringan acceleration of about 0.2 m/s² for a 5 μm offset in the first axisdirection when taking a settling time associated with the linear motor112 into account. This acceleration may be contrasted against theacceleration that would be required to account for the full differencebetween the offsets 730 and 732 shown in FIG. 7 which would be very muchgreater. Differences in orientation between display substrates may reach1 mm in some cases, which under the conditions above would require anacceleration of about 40 m/s² to correct by repositioning of the imaginghead 108 alone. Accordingly, the embodiment of the process shown in FIG.9, which provides a combination of offsetting the digital mask whilecorrecting for any residual offset by moving the imaging head to alesser degree, would be easier to implement due to the lower requiredfirst axis acceleration.

The embodiment described above in connection with FIG. 9, has describedin connection with an imaging head 108 that does not move in the firstaxis 110 while imaging each display substrate. However, the displaysubstrates 602 and 604 shown in FIG. 9 each have an angular rotationwith respect to the second axis 124, which causes successive shifts inthe placement of the color filter elements within the pixels asdescribed earlier in connection with the process 800. In anotherembodiment, the repositioning described above may be combined with aslow scan of the imaging head 108 in the direction of the first axis toalso compensate for the rotation of the display substrates 602 and 604thereby reducing the successive shifts between filter elements onsubsequent pixels.

For example, a coordinated scan to match rotation angle θ=0.5° for oneof the display substrates, with a 2 m/s second axis velocity of relativedisplacement, would require a scan velocity in the first axis directionof 0.017 m/s. The linear motor 112 and controller 140 would have about10 milliseconds to initiate this change which would require anacceleration of about 3.4 m/s². Such an acceleration would also bereasonable for a precision flat bed imaging system, such as that showngenerally in FIG. 1.

However, in other embodiments the rotation angle associated with thedisplay substrates may be significantly higher than 0.5°, thereforerequiring a larger gap between the displays in order to providesufficient time for adapting the coordinated motion from display todisplay. Alternatively, if the gap between displays is constrained thenhigher acceleration would have to be provided by the first axis linearmotor 112, which may increase cost and complexity of the first axislinear drive.

In general, the relative displacement between the display substrates andthe digital imaging system in the direction of the second axis wouldinclude a first pass in a direction aligned with the second axis 124 anda second pass or return pass in a direction opposite to the direction ofthe first pass. In some embodiments, the imaging head 108 is offset by awidth of the swath 136 while the direction of motion is being changed tofacilitate deposition of filter elements on the second pass, therebyincreasing throughput. In other embodiments the filter elementsdeposited during the second pass may be visibly different to the filterelements deposited during the first pass, and in such cases depositionmay only be enabled during the first pass. Referring to FIG. 10, inanother alternative embodiment, the time provided for accelerating theimaging head 108 between displays may be increased by depositing filterelements only on selected ones of the display substrates (for examplesubstrates 602 and 606) on the first pass along the swath 1000 and thenimaging remaining display substrates (for example the substrate 604) onthe second pass generally along the swath 1000. One advantage associatedwith this embodiment, is that a distance 1002 within which the imaginghead 108 may be accelerated for repositioning, as described above inconnection with the FIG. 9 embodiment, is significantly increased. Thisreduces the associated acceleration requirements and provides more timefor settling and initiation of a scan velocity in the first axisdirection. In the embodiment shown in FIG. 10, the imaging head 108 isinitially positioned to deposit filter elements on display substrate 602in the first pass of the swath 1000, and is then repositioned during thetime taken to traverse the distance 1002, as generally described abovein connection with the embodiment of FIG. 9. Deposition of filterelements then occurs on the substrate 606, and when completed, themotion of the image head in the first pass direction is decelerated andthe imaging head is accelerated up to imaging speed in the second passdirection. Accordingly, a distance 1004 is available during which theimaging head 108 may be accelerated up to imaging speed in the secondaxis 124, and accelerated in the first axis 110 to permit repositioningfor imaging the display substrate 604 during the second pass. Fortypical display substrate sizes and disposition on the chuck 116, thisembodiment further reduces the acceleration required in the first axis110 over the FIG. 9 embodiment.

Once deposition of the filter elements on the display substrate 604 iscompleted along the swath 1000, the distance 1006 is then available formoving the imaging head 108 into position for the next swath 1008.Deposition of filter elements for the swath 1008 may proceed in the samefashion.

The embodiment shown in FIG. 10 may be used in configurations wherethere are at least two display substrates along the second axis 124, butis also applicable to configurations of any other number of substrates.While in FIG. 10, the embodiment has been described in connection wherefilter element deposition occurs on odd numbered displays during thefirst pass and even numbered displays during the second pass, otherconfigurations may also be implemented where the display substrates arenot regularly arranged, for example in cases where some displays areremoved.

Interleaving

Referring to FIG. 11, an alternative deposition embodiment that may becombined with several of the above disclosed embodiments is shown. Inthis embodiment deposition for filter elements along a swath 1100 occurson each of the display substrates 602, 604, and 606 during a first passof the imaging head 108, but only every second deposition location isactuated on this first pass. Accordingly, incomplete filter elementswould be deposited during the first pass. During the second pass, theremaining portions of the filter element are filled in by actuating theappropriate deposition locations in the second pass along the swath1100.

Alternatively, on completion of the first pass the imaging head may bemoved over by the spacing between deposition locations to align theimaging head with a second swath 1102 and during the second pass, theremaining portions of the filter element would be filled in by actuatingthe appropriate deposition location in the second swath 1102.

The above interleaved deposition configurations have the advantage ofcausing each filter element to be deposited in two passes of the imagehead 108 in opposite directions, thus reducing the effect of depositiondifferences between the first and second passes, as described above inconnection with the embodiment of FIG. 10. Additionally, some imagingsystems and/or media result in imperfect transfer of colorant to thedisplay, which may be particularly pronounced when imaging solid areassuch as occur within filter elements. The above interleaved depositionmay also reduce such effects.

In the above description, the interleaving is described on the basis ofa single deposition location, but in other embodiments the interleavingmay involve more than a single deposition location.

Filter Element Shaping

The above embodiments have generally been described in connection withan imaging system that is configured to generate deposition locationsthat have similar dimensions in the first and second axis. However, asnoted above in connection with the example of the Kodak SQUARESpot®imaging head, the generated beams 128 have a generally rectangularprofile of and may be controlled to deposit filter material in thesecond axial direction with greater precision than is possible in thefirst axial direction.

Referring to FIG. 12, in an alternative embodiment the imaging head 108is configured to provide second deposition locations 1200 along thesecond axis 124 that are more closely spaced than the first depositionlocations along the first axis. An identified pixel 1202 has associatedfirst axis extents and second axis extents in the direction of therespective first and second axes as shown in FIG. 12. Under theseconditions, placement of the filter element along the second axis 124may be more precisely controlled than the placement of the filter alongthe first axis 110. In this embodiment, block 808 of the process 800shown in FIG. 8, may be implemented to cause selection of depositionlocations differently in the first and second axes 110 and 124. In oneembodiment, the first axis deposition locations are selected to providean increased spacing between the filter element 1204 and first axisextents 1206 and 1208 of the pixel 1202. In the embodiment shown in FIG.12, more than a single deposition location remains unselected in thepixel 1202, which may be contrasted with the embodiment shown in FIG. 7where in most cases only a single deposition location remainedunselected in proximity to the pixel extents. However, in mostembodiments the deposited filter elements should meet a coveragecriterion, such as a target coverage area, to cause each pixel to havesubstantially similar brightness to other pixels of the same color.Accordingly, in compensation for the increased spacing in the first axisdirection 110, second deposition locations along the second axis 124 areselected to provide a reduced spacing between the filter element and thesecond axis extents 1210 and 1212, such that the selection of first andsecond deposition locations together meets the coverage criterionassociated with the filter element 1204 within the pixel 1202. Thisembodiment may also be combined with other described embodiments, suchas the embodiments described in connection with FIGS. 9-11.

The embodiment shown in FIG. 12 also further facilitates introduction ofa random variation in placement of the filter elements in the first andsecond axes in order to disrupt regular patterns that occur in filterelement placement due to the selection of deposition locations byproviding a greater spacing between the filter element 1204 and thefirst axis extents. Since the deposition precision in the second axisdirection is increased over the first axis, more precise placement ofthe filter element along the second axis 124 has the effect of providinggreater latitude for random variations in placement along the first axis110.

In other embodiments, random variations may be introduced in spacingfrom the first axis extents 1206 and 1208 in subsequent identifiedpixels. Such random variations may be compensated by selecting thesecond deposition locations along the second axis 124 to meet thecoverage criterion associated with the filter element. While in thedescribed embodiments, a shape associated with the filter elements hasgenerally been disclosed to be rectangular; in other embodiments theshape of the filter element may have a shape that is other than squareor rectangular, or even an irregular shape.

Conditioning of Deposited Filter Elements

Filter elements that are deposited using any of the above embodiments,may result in the transferred filter element having a rough surfacetexture. This effect has been particularly noticeable when using thermaltransfer donors, since the transfer at each deposition location from thedonor may be imperfect. For some applications, the rough surface texturemay be undesirable and may cause difficulties. For example, in the caseof color filter elements for displays, optical effects due to roughsurface texture may cause degradation in the quality of the imagedisplayed by the display. It is believed that reflective displays areparticularly affected by such optical effects.

In another embodiment of the invention, once the selective deposition ofthe filter element material has been completed, a further step may beintroduced which involves selectively exposing the deposited filtermaterial to thermal laser radiation to condition the deposited filtermaterial. The deposited filter elements thus undergo an annealingprocess, which it is believed causes the temperature of the filterelement material to be raised above a glass transition temperature ofthe material, thus permitting the material to at least partially re-flowto smooth the rough surface texture. Once cooled, the filter elementmaterial surface has improved smoothness due to the re-flow.

Selective conditioning using the same imagewise controllable lasersource may have several advantages over a separate annealing step.Introducing a separate annealing process would add another step to theprocess, and would also involve additional annealing equipment. Therealso may be the possibility of damage to the display substrate byraising the temperature of the entire substrate sufficiently to causeannealing. These problems are both addressed by the selectiveconditioning described herein, since in general only the color filterelement material will be raised to the annealing temperature reducingthe risk of damage to the underlying pixels. Furthermore, for thermaltransfer, the laser wavelengths that are suitable for enabling lasertransfer, would generally be well absorbed by the filter elementmaterial and would thus be particularly effective in raising the filterelement material to the annealing temperature.

Referring to FIG. 13, a process for directing the microprocessor 302shown in FIG. 3 to carry out the conditioning process in accordance withone embodiment of the invention is shown generally at 1300. The processbegins at block 1302, which directs the microprocessor 302 to controlthe digital imaging system 100 (shown in FIG. 1) to cause deposition ofthe filter material at selected deposition locations, as described inthe embodiments disclosed above. Block 1304 then optionally directs themicroprocessor 302 to adjust the intensity level of the laser source toa level suitable for annealing. Such a level may be provided byincreasing or reducing the laser power or by adjusting at attenuationlevel associated with a modulator disposed to control radiationgenerated by the laser source, for example. In embodiments where theconditioning occurs at the same laser intensity or power level, block1304 may be omitted.

The process 1300 then continues at block 1306, which directs themicroprocessor 302 to read the digital mask information stored in thestore 356 of variable memory 306. In embodiments where annealing of allcolor filter elements of different colors are to be annealed at the sametime, separate digital masks associated with each of the color filterelements would additionally require processing to provide a combineddigital mask for all colors. Block 1308 then directs the microprocessor302 to generate control signals at the ports 142, 144, and 146 forcontrolling the digital imaging system to cause the conditioning of thefilter element material, at the deposition locations.

In one embodiment, the same laser source used for deposition of thefilter elements is also used to perform the selective exposure forconditioning the filter elements. In other embodiments, a differentlaser source having a different wavelength may be used to perform theselective exposure for conditioning the filter elements.

The above embodiments provide methods and associated apparatus forforming color filter elements either directly on pixels of a displaysubstrate or on a glass or non-glass substrate. Direct deposition on thefilter elements has one associated advantage of being performed duringdeposition, thus eliminating an additional alignment step. Furthermore,an additional glass layer carrying the filter element is eliminated fromthe resulting display product, thus reducing the weight of the displayproduct. Direct deposition embodiments also generally result in lessscattering of transmitted or reflected light, potentially providingbetter color display performance.

While specific embodiments of the invention have been described andillustrated, such embodiments should be considered illustrative of theinvention only and not as limiting the invention as construed inaccordance with the accompanying claims.

1. A method for forming filter elements on at least one displaysubstrate using a digital imaging system operable to selectively depositfilter material at a plurality of deposition locations, the methodcomprising: receiving orientation information defining a disposition ofa plurality of pixels associated with the at least one displaysubstrate; identifying pixels in said plurality of pixels that are toreceive filter material for forming a filter element on the pixel;selecting deposition locations within each of said identified pixels inaccordance with said orientation information to meet an alignmentcriterion associated with placement of the filter element within saidpixel; and controlling the digital imaging system to cause deposition ofthe filter material at said selected deposition locations.
 2. A digitalimaging system operable to selectively deposit filter material at aplurality of deposition locations to form filter elements on at leastone display substrate, the digital imaging system comprising acontroller operably configured to: receive orientation informationdefining a disposition of a plurality of pixels associated with the atleast one display substrate; identify pixels in said plurality of pixelsthat are to receive filter material for forming a filter element on thepixel; select deposition locations within each of said identified pixelsin accordance with said orientation information to meet an alignmentcriterion associated with placement of the filter element within saidpixel; and control the digital imaging system to cause deposition of thefilter material at said selected deposition locations.
 3. A method forforming filter elements on at least two display substrates using adigital imaging system operable to selectively deposit filter materialat a plurality of deposition locations, said deposition locationscomprising first deposition locations generally aligned along a firstaxis of the display substrates and second deposition locations generallyaligned along a second axis of the display substrates, the at least twodisplay substrates being disposed in succession along said second axis,the method comprising: receiving orientation information defining adisposition of a plurality of pixels associated with each of saiddisplay substrates with respect to the first and second axes;identifying pixels in said plurality of pixels that are to receivefilter material for forming a filter element on the pixel; selectingdeposition locations within each of said identified pixels in accordancewith said orientation information to meet an alignment criterionassociated with placement of the filter element within said pixel;computing an offset associated with said plurality of pixels in adirection of the first axis for at least one of said display substrates;determining a residual portion of said offset that cannot be compensatedby said selection of said deposition locations; controlling the digitalimaging system to cause deposition of the filter material at saidselected deposition locations by: causing respective relativedisplacements between the display substrates and the digital imagingsystem in a first pass in a first direction aligned with the second axisand a second pass in a second direction opposite to said firstdirection; causing deposition of filter material on alternate ones ofsaid at least two display substrates during said first pass and causingdeposition of filter material on remaining ones of said at least twodisplay substrates on said second pass; and causing the digital imagingsystem to be repositioned relative to said display substrates by saidresidual portion of said offset while disposed between at least one ofsaid alternate ones of said display substrates in said first pass orsaid remaining ones of said display substrates during said second pass.4. A digital imaging system for forming filter elements on at least twodisplay substrates by selectively depositing filter material at aplurality of deposition locations, said deposition locations comprisingfirst deposition locations generally aligned along a first axis of thedisplay substrates and second deposition locations generally alignedalong a second axis of the display substrates, the least two displaysubstrates being disposed in succession along said second axis, thedigital imaging system comprising a controller operably configured to:receive orientation information defining a disposition of a plurality ofpixels associated with each of said display substrates with respect tothe first and second axes; identify pixels in said plurality of pixelsthat are to receive filter material for forming a filter element on thepixel; select deposition locations within each of said identified pixelsin accordance with said orientation information to meet an alignmentcriterion associated with placement of the filter element within saidpixel; compute an offset associated with said plurality of pixels in adirection of the first axis for at least one of said display substrates;determine a residual portion of said offset that cannot be compensatedby said selection of said deposition locations; control the digitalimaging system to cause deposition of the filter material at saidselected deposition locations by: causing respective relativedisplacements between the display substrates and the digital imagingsystem in a first pass in a first direction aligned with the second axisand a second pass in a second direction opposite to said firstdirection; causing deposition of filter material on alternate ones ofsaid at least two display substrates during said first pass and causingdeposition of filter material on remaining ones of said at least twodisplay substrates on said second pass; and causing the digital imagingsystem to be repositioned relative to said display substrates by saidresidual portion of said offset while disposed between at least one ofsaid alternate ones of said display substrates in said first pass orsaid remaining ones of said display substrates during said second pass.